WO2003102941A1

WO2003102941A1 - Optical recording medium, optical information processor and optical recording/reproducing method

Info

Publication number: WO2003102941A1
Application number: PCT/JP2003/006566
Authority: WO
Inventors: Hiroaki Yamamoto; Teruhiro Shiono; Tatsuo Ito; Seiji Nishino; Sadao Mizuno
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2002-05-31
Filing date: 2003-05-26
Publication date: 2003-12-11
Also published as: EP1515322A1; CN100358030C; EP1515322A4; US7656777B2; CN1659641A; JP4199731B2; JPWO2003102941A1; AU2003241782A1; EP1515322B1; US20050207328A1; DE60336316D1

Abstract

An optical recording medium which is a multilayer optical recording medium including a plurality of recording layers and records or reproduces information by the irradiation of light having a wavelength of λ0. At least one recording layer out of a plurality of recording layers includes a variable absorption film. The variable absorption film contains a material in which an electron energy has a band structure, and the absorption end of an absorption spectrum moves toward a longer wavelength side with a rise in temperature when light is absorbed by transition between electron bands, has a first absorptance to light having a wavelength of λ0 when a film temperature is a first temperature (application environment temperature), and has a second absorptance higher than the first absorptance to light having a wavelength of λ0 when a film temperature is a second temperature higher than the first temperature.

Description

Description Optical recording medium, optical information processing device and optical recording / reproducing method

The present invention relates to an optical recording medium such as an optical disk or an optical card on which information is optically recorded / reproduced, an optical information processing apparatus for recording / reproducing information on / from an optical recording medium, and an optical recording / reproducing method. Things. Background art

In recent years, as the information society has advanced, large-capacity external storage devices have been desired. In optical information recording, there is a diffraction limit determined by the wavelength of light and the numerical aperture of the objective lens. Therefore, there has been a limit in increasing the recording density by reducing the size of the recording pit. In order to solve such a problem, a multilayer optical recording medium having a plurality of recording layers has been proposed (for example, Japanese Patent Application Laid-Open No. H5-1151591). However, since the recording layer used in such a multilayer optical recording medium is a translucent film having a constant reflectance and transmittance with respect to light, a recording layer other than the target recording layer is used. There was light loss due to light reflection at the recording layer. In addition, if the upstream side in the traveling direction of the incident light is up and the downstream side is down, the transmitted light reaches the layer located below the target recording layer, which causes further light loss. .

Therefore, in order to solve such a problem, a multilayer optical recording medium using a nonlinear material having a nonlinear optical characteristic in a recording layer has been proposed (for example, Japanese Patent Application Laid-Open No. 2000-35929). .).

FIG. 11 shows a cross-sectional configuration of a conventional multilayer optical recording medium. The optical recording medium of FIG. 11 includes a first light transmitting film 10 and a second light transmitting film It has a first recording layer 12 and a second recording layer 16 formed at a position facing the first recording layer 12 with the second light transmitting film 14 interposed therebetween. Further, the first recording layer 12 is provided with a guide groove 12A. The first recording layer 12 is formed of a non-linear reflection material having a reflectivity that increases non-linearly as the light intensity increases. Non-linear reflective materials having such properties include a—Si, InSb, ZnTe, ZnSe, CdSSe, GaAs, and GaSb. When forming such a non-linear reflective material in the first recording layer 1 2, the first recording layer 1 2, a _{i (n- n s) / (} n + n s) I reflectivity varies on ² Niyotsu Have. Here, _ns is the refractive index of the light transmitting film 10 and the light transmitting film 14, and n is the refractive index of the first recording layer 12 which is a non-linear reflection material. The non-linear reflection material used here is a material that causes a phenomenon in which the refractive index changes depending on the light intensity, that is, a material having a so-called nonlinear optical effect.

The optical characteristics of such an optical recording medium will be described. When the first recording layer 12 is accessed, a light beam applied to the first recording layer 12 becomes relatively strong because a light spot is formed on the first recording layer 12. At this time, it is assumed that the reflectance of the first recording layer 12 is, for example, 40%. On the other hand, when the second recording layer 16 is accessed, the irradiated light spot is formed on the second recording layer 16 so that the light irradiated on the first recording layer 12 is relatively weak. . Assuming that the reflectance of the first recording layer 12 at this time is, for example, 30%, the first recording layer 12 reflects 30% of incident light and transmits 70% to the second recording layer 16 side. become. Therefore, the second recording layer 16 can be accessed efficiently.

However, in the above-described conventional technique, the change in reflectance is only 10%, from 30% to 40%. This is a limitation due to the use of a material having a nonlinear optical effect for the first recording layer 12 and the second recording layer 16. There is a problem that the amount of light is insufficient for multi-layering. Further, the above-mentioned conventional technology is for a read-only memory (ROM) in which information is recorded in advance. Therefore, it was difficult to secure the energy required for information recording by using this technology and realize a recordable multilayer optical recording medium. Disclosure of the invention

The first optical recording medium of the present invention is a multilayer optical recording medium including a plurality of recording layers for recording or reproducing information by irradiating light having a wavelength of λ0, wherein at least one of the plurality of recording layers is used. One of the recording layers includes a variable absorption film. The variable absorption film has a band structure in which the energy of electrons has a band structure, and the absorption edge of the absorption spectrum becomes longer as the temperature rises in light absorption due to the transition between the bands of electrons. It contains a material that moves to the wavelength side, and has a first absorptance for light having a wavelength λ0 when the film temperature is the first temperature, and the film temperature is higher than the first temperature At the second temperature, it has a second absorptance higher than the first absorptivity for light having a wavelength λθ.

The second optical recording medium of the present invention is a multilayer optical recording medium including a plurality of recording layers for recording or reproducing information by irradiating light having a wavelength λ0, wherein at least one of the plurality of recording layers is used. One recording layer includes: a variable absorption film; and a recording film disposed close to the variable absorption film so that heat of the variable absorption film can be transmitted. The energy of the electrons has a band structure, and includes a material in which the absorption edge of the absorption spectrum moves to the longer wavelength side as the temperature rises in the light absorption due to the inter-band transition of the electrons. It is transparent to light having a wavelength λ0 at a temperature, and has a wavelength of 0 at a second temperature where the film temperature is higher than the first temperature. When the film temperature is the first temperature, the recording film absorbs at least a part of the light having the wavelength λ0 and generates heat, and the optical characteristic changes at a predetermined temperature. Features.

An optical information processing apparatus according to the present invention includes: the first or second optical recording medium according to the present invention; a light source that emits light having a wavelength of λ0; and the light emitted from the light source. A light-collecting optical system that collects light on a target recording layer included therein; and a photodetector that detects light reflected by the optical recording medium, wherein the variable absorption is performed by irradiating the light emitted from the light source. A light absorption increasing portion is formed on the film, and information is recorded or reproduced by increasing the temperature of the light absorption increasing portion.

An optical recording / reproducing method according to the present invention is an optical recording / reproducing method for recording and reproducing information on the first or second optical recording medium according to the present invention, wherein light having a wavelength λ 0 Concentrating light on the layer, forming a light absorption increasing portion in the variable absorption film included in the recording layer, and increasing / decreasing the temperature of the light absorption increasing portion, thereby recording / reproducing information on / from the recording layer. Is characterized by

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an explanatory diagram illustrating a cross-sectional configuration of an optical recording medium and a state in which information is recorded / reproduced in Embodiment 1 of the present invention.

FIG. 2 is a diagram illustrating an example of a spectral absorption coefficient curve of the variable absorption film included in the optical recording medium according to the first embodiment of the present invention.

Figure 3 is a diagram illustrating a spectral absorption curve of B i ₂ 0 _3.

Figure 4 is a diagram showing temperature characteristics of the absorption rate of B i ₂ 0 _3.

FIG. 5 is a diagram showing another example of the spectral absorption coefficient curve of the variable absorption film included in the optical recording medium according to Embodiment 1 of the present invention. FIG. 6 is an explanatory diagram showing a cross-sectional configuration of an optical recording medium according to Embodiment 2 of the present invention and a state in which information is recorded and reproduced.

FIG. 7 is a diagram showing a spectral absorption curve of As ₂ S ₃ .

FIG. 8 is an explanatory diagram showing a state in which super-resolution reproduction is performed on one recording layer of the optical recording medium according to the first embodiment of the present invention.

FIG. 9 is a diagram showing the relationship between the light intensity, the extinction coefficient of the variable absorption film, and the light spot region.

FIG. 10 is an explanatory diagram illustrating a schematic configuration of an optical information processing apparatus according to an embodiment of the present invention.

FIG. 11 is a cross-sectional view of a conventional multilayer recording medium. BEST MODE FOR CARRYING OUT THE INVENTION

According to the first and second optical recording media of the present invention, by providing the variable absorption film, it is possible to secure energy required for recording even in a multilayer optical recording medium including a plurality of recording layers. As a result, large capacity can be realized. Further, a sufficient amount of reproduced light can be obtained when reproducing the recorded information.

In the first optical recording medium of the present invention, it is preferable that the variable absorption film absorbs light having a wavelength λ 0 at the first temperature by light absorption due to an interband transition of electrons in the material. However, light having a wavelength λ 0 may be absorbed by light absorption by impurities.

In the first optical recording medium of the present invention, the recording layer including the variable absorption film further includes a recording film, and the recording film includes the variable absorption film to such an extent that heat of the variable absorption film can be transmitted. It is preferable that the optical characteristics be changed close to the film and be changed at a predetermined temperature. Since the recording material can be selected appropriately, recording stability can be improved, recording efficiency can be further improved, and the amount of reproduced light can be improved. This is because a further increase can be realized.

In the first optical recording medium of the present invention, it is preferable that the variable absorption film changes its optical characteristics at a predetermined temperature. This is because the variable absorption film can also function as a recording film, eliminating the need to separately form a recording film. In the first optical recording medium of the present invention, the plurality of recording layers include n layers (n is an integer of 2 or more), and each of the plurality of recording layers includes the variable absorption film. When the m-th recording layer is the m-th recording layer (where m is an integer of l <m≤n), at the first temperature, the m-th recording layer is exposed to light having a wavelength λθ. and absorptance a _m of the variable absorption film included in the m-th recording layer and the reflectance R _m preferably satisfy the following relationship.

R _m = R _n / (n-m + 1)… (1)

A _m = A no (n -m + 1)… (2)

By satisfying the above expressions (1) and (2), the amount of light absorbed by each recording layer can be made substantially the same without changing the intensity of the recording light for each recording layer.

In the first and second optical recording medium of the present invention, the variable absorption film, and B i ₂ 0 _3, and A s ₂ S _3, and mixed glass including T e 0 ₂ and N a ₂ 0, Mixed glass containing T e〇 ₂ and W〇 ₃ , mixed glass containing T e〇 ₂ and F e _{2 2} ₃ , mixed glass containing T e 0 ₂ and C u〇, T e 〇 ₂ , C a Mixed glass containing O and WO ₃ , aluminum gallium arsenide (A 1 G a As) compound semiconductor, and aluminum gallium indium arsenide (A 1 G a In A s) compound semiconductor It is preferable to include at least one selected from the group consisting of

In the first and second optical recording media of the present invention, it is preferable that the first temperature is a use environment temperature of the optical recording medium.

According to the optical information processing apparatus of the present invention, the first or second optical recording of the present invention Information can be recorded on a medium, and a sufficient amount of reproduced light can be obtained when the recorded information is reproduced.

In the optical information processing apparatus according to the present invention, the intensity of the light emitted from the light source is adjusted so that the light absorption increasing portion formed on the variable absorption film is smaller than a spot size of the collected light. It is preferable to further include a control unit for controlling the pressure. This is for performing super-resolution reproduction.

According to the optical recording / reproducing method of the present invention, information can be recorded on the first or second optical recording medium of the present invention, and when reproducing the recorded information, a sufficient reproducing light amount is required. You can also get.

In the optical recording / reproducing method of the present invention, the intensity of the light is controlled such that the light absorption increasing portion formed on the variable absorption film is smaller than a spot size of the light to be collected. preferable. This is to perform super-resolution reproduction.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)

FIG. 1 shows a cross-sectional configuration of the optical recording medium according to the first embodiment of the present invention. This optical recording medium has a first recording layer 7 on a substrate 7 0 1 from the light L 0 incident side.

51, a second recording layer 752, and a final recording layer 754 are multilayer optical recording media provided in this order. Separation layers 731 and 732 are provided between the recording layers. The light L 0 is light having a wavelength λ 0, which is irradiated when information is recorded or reproduced on the optical recording medium of the present embodiment.

The first recording layer 751 and the second recording layer 752 have the same film configuration, and from the light L0 incident side, the recording film 7 2 1 (7 2 2) and the variable absorption film 7 9 1 ( 7 9

2) are provided in this order.

Further, the second recording layer 752 is sandwiched between the second recording layer 752 and the separation layer 7332, and a final recording layer 754 including a recording film 723 and a reflection film 72 is arranged. Each of the recording layers 751, 752, and 754 is provided with a guide groove having an uneven shape, and the guide groove is used to specify a recording position.

The separation layers 731 and 732 are made of a neo-material transparent to the light L0, and for example, PMMA (polymethyl methacrylate) can be used.

The recording films 72 1 and 722 included in the first recording layer 751 and the second recording layer 752 are substantially transparent to light L 0 having a wavelength λ 0 used as recording light and reproduction light, and have a predetermined temperature. It has the property of changing from an unrecorded state to a recorded state. Here, the recorded state refers to a state in which the optical characteristics have changed from the unrecorded state. For example, the optical characteristics are changed due to a physical change such as a change in refractive index, a change in extinction coefficient, a change in shape, or a chemical change. A state that has changed. The recording films 721, 722 need only be made of a material that is substantially transparent to the light L0 of the wavelength λ0 and that is formed of a material whose optical properties change at a predetermined temperature. For example, a heat-polymerizable resin, a heat-deformable resin, and a heat-decomposable resin can be used. Specifically, for example, when the wavelength λ 0 = 405 nm, for example, the organic dye 2— [7— (1,3-dihydro-5-methoxy1,3,3-trimethyl-2H—indole-2 —Ilidene) 1,3,5-Heptatrienyl] — 5-Methoxy-1,3,3-trimethylol 3 H-indolium perchlorate (for example, NK—2882 manufactured by Hayashibara Biochemical Laboratory Co., Ltd.) ) Etc. can be used. When the wavelength is λ 0 = 630 nm, for example, 2- [2- [4-1 (dimethylamino) phenyl] ethenyl] naphtho [1,2-d] thiazole (for example, Hayashibara Co., Ltd.) For example, NK-188 6) manufactured by NIMS can be used. In the case of an acrylic-based thermopolymerizable resin, a thermally deformable resin such as PMMA or polyester, or a thermally decomposable resin such as benzotriazole, either light having a wavelength of 405 nm or a wavelength of 630 nm is used. It can also be used for The variable absorption films 791 and 792 included in the first recording layer 751 and the second recording layer 752 have a band structure in which the energy of the electrons has a band structure, and the light absorption due to the light absorption due to the transition between the bands of the electrons. The absorption edge of the vector is made of a material that moves to the longer wavelength side (lower energy side) as the temperature rises. Note that the absorption edge is the edge on the low energy side of the absorption spectrum.

FIG. 2 shows an example of a spectral absorption curve of the variable absorption films 791 and 792 in the present embodiment. As shown in FIG. 2, the variable absorption films 79 1 and 792 are films in which the spectral characteristics of the absorptance change according to the temperature. When the film temperature is normal temperature, the variable absorption films 79 1 and 792 are lower than the light of wavelength λ 0. Indicates the absorptance (first absorptivity). When the film temperature increases, the absorptivity moves to the longer wavelength side, so the absorptivity for light of wavelength λ 0 increases and the absorptivity (second absorptivity) It is made of a material having the properties shown. Therefore, when the light L 0 having the wavelength λ 0 is irradiated as the recording light or the reproduction light, the variable absorption films 791 and 792 first absorb light with a small absorption rate, and the temperature increases due to the light absorption. As the absorption rate increases, light will be absorbed at a higher absorption rate at temperatures higher than room temperature. In this specification, the normal temperature refers to a temperature at which the optical recording medium is used, that is, an environment temperature at which the optical recording medium is used. In addition, the light absorption of the variable absorption films 791 and 792 at a normal temperature at the wavelength λ 0 is not limited to the electron absorption of the material having the above properties contained in the variable absorption films 791 and 792. In addition to the absorption due to the inter-band transition, the absorption due to impurities may be included.

The variable absorption films 791 and 792 need to include a material having the above-described properties with respect to the light L0 having the wavelength λ0. 0 = for _{40 5 nm, B i 2 0} 3, T e 0 2 and mixed glass with N a ₂ O, mixed glass with T e 0 ₂ and W_〇 _3, Ding 6_Rei ₂ and 6 ₂ 〇 ₃ and mixing glass, mixing glass with T E_〇 ₂ and CuO are exemplified, its B i ₂ 0 ₃ Among preferred. Further, when the wavelength λ 0 = 630 nm, As ₂ S ₃ , AlGaAs compound semiconductor, A1GaInAs compound semiconductor and the like can be mentioned, among which As ₂ S ₃ is preferable.

The recording film 723 included in the final recording layer 754 is made of a material that absorbs light L 0 of wavelength λ 0, and has a property of changing from an unrecorded state to a recorded state due to absorption of light L 0 of wavelength λ 0. As a material of the recording film 723, for example, tellurium oxide (TeO _x ) can be used. Further, as the reflective film 702, a metal film containing A1 or the like can be used.

Next, an operation of recording and reproducing information on the optical recording medium according to the present embodiment will be described.

FIG. 10 shows an example of an optical information processing apparatus for recording or reproducing information on or from the optical recording medium of the present embodiment. Hereinafter, a method of recording and reproducing information on and from the optical recording medium of the present embodiment using this optical information processing apparatus will be described.

The optical information processing apparatus of the present embodiment is provided with a semiconductor laser 101 as a radiation light source, and a collimating lens 102 and a polarizing beam splitter in an optical path from the semiconductor laser 101 to the optical recording medium 105. 107, a 14-wave plate 115, and an objective lens 103 fixed to an actuator 112 are arranged. At the time of recording, the light emitted from the semiconductor laser 101 is converted into parallel light by the collimating lens 102, passes through the polarizing beam splitter 107, is further converted into circularly polarized light by the 1/4 wavelength plate 115, and then is converted into the objective lens. The light is condensed on the optical recording medium 105 by 103 and information is recorded. At the time of reproduction, reflected light of light condensed on the optical recording medium 105 is used. The light reflected by the optical recording medium 105 is converted into parallel light by the objective lens 103, converted into linearly polarized light by the 1Z4 wavelength plate 115, and reflected by the polarization beam splitter 107. Polarized beam The light reflected by the splitter 107 is converted into convergent light by the detection lens 104, and then diffracted and separated by the hologram element 18 1 (L 1, L 2). Is detected. The photodetector 190 has a plurality of light receiving areas of detection areas, and a signal detected in each area is input to the electric circuit 504. The electric circuit 504 extracts a data signal from the input signal. As a result, information is reproduced. Further, the electric circuit 504 obtains a service signal for controlling the position of the objective lens 103, and drives the actuator 112. Note that the electric circuit 504 controls the output of the semiconductor laser so that the quality of the obtained data signal is the best.

FIG. 1 shows a state in which information is recorded (or reproduced) on the second recording layer 752, for example. The light L 0 is a laser beam having a wavelength λ 0 and is focused on the second recording layer 752 of the optical recording medium by the objective lens 103 (see FIG. 10) of the optical information processing device. The position of the objective lens 103 is controlled by the actuator 112 (see FIG. 10).

First, the operation for recording information will be specifically described. The light L0 passes through the substrate 71, the first recording layer 751, and the separation layer 731, and enters the second recording layer 752. Light 0 is slightly absorbed by the variable absorption film 791 when passing through the first recording layer 751, but since the light 0 is not condensed on the surface of the variable absorption film 791, the energy density of heat generation is Low, the variable absorption membrane 791 is kept at almost room temperature. Therefore, the light L0 can efficiently pass through the first recording layer 751, and further pass through the separation layer 731, and reach the second recording layer 752.

The light L 0 incident on the second recording layer 752 passes through the recording film 72 2 and is incident on the variable absorption film 792. Since the variable absorption film 792 has a low absorptance to the light L 0 having the wavelength λ 0, it absorbs a part of the incident light L 0 and generates heat. Since the light L0 is condensed by the variable absorption film 792, the heat High energy density. For this reason, the temperature of the variable absorption film 792 at the light L0 incident portion locally increases. Due to this temperature rise, the absorptivity of the variable absorption film 792 for the light L0 increases, and the light absorption increasing portion 741 is formed in the variable absorption film 792. The light absorption increasing section 741 further rises in temperature as the absorption of the light L0 increases. Eventually, the temperature rise of the light absorption increasing portion 741 stops when the heat generation in the light absorption increasing portion 741 of the variable absorption film 792 and the amount of heat diffusion to the recording film 7222 and the like are balanced. I do.

The heat generated in the light absorption increasing portion 741 of the variable absorption film 792 diffuses to the recording film 722. Information is recorded on the recording film 722 by the temperature rise of the recording film 722 due to the diffused heat. That is, due to this thermal diffusion, the temperature of the recording film 722 reaches a predetermined temperature (hereinafter, referred to as a recording temperature) at which the optical characteristics of the recording film 722 change, and the optical characteristics change at a portion where the recording temperature is reached. A part (recording mark) is formed.

Next, an operation of reproducing information recorded on the recording film 722 of the second recording layer 752 will be described.

Increasing the temperature and the absorptance of the variable absorption film 792 by the incident light L0 is the same as during recording. The difference from the recording is that the intensity of the light L0 is controlled so that the temperature rise of the recording film 722 due to the heat generated by the variable absorption film 792 is suppressed below the recording temperature. The principle of reading information recorded on the optical recording medium of the present embodiment is as follows.

The reflectance R of light L 0 at the interface between the recording film 722 and the variable absorption film 792 is represented by the following equation. In the following equation, ηθ is the refractive index of the recording film 722, n is the refractive index of the variable absorption film 792, and k is the extinction coefficient of the variable absorption film 792.

R = ((N— η θ) / (N + n 0)) ²

N = (n ² + k ² ) ^1/2 "(4) In the variable absorption film 792, as the temperature rises from room temperature, the absorptivity for light L0 increases, that is, the extinction coefficient increases. As a result, according to Equations (3) and (4), the reflectance R increases and the amount of reflected light increases. Since this reflected light is modulated by the recording mark of the recording film 722 and used for detecting information, a signal can be detected with high efficiency by increasing the amount of reflected light.

Although the recording and reproduction of information on the second recording layer 752 has been described above, the recording and reproduction of information on the first recording layer 751 is performed by setting the light condensing position of the light L0 to the first recording layer. By setting it to 751, information can be recorded and reproduced in the same manner.

Recording and reproduction of information on the final recording layer 754 are performed by setting the focal position of the light L0 to the final recording layer 754. The light 0 enters the first recording layer 751 and the second recording layer 752 before reaching the final recording layer 754, but in the variable absorption films 791 and 792, the light L0 is Since it is not focused, the heat generation area is dispersed and the temperature rise is small. Therefore, the light absorption increasing portion is not formed, and the light L 0 is transmitted. At the time of recording information, the recording film 723 absorbs the light L0, causing a temperature rise to form a recording mark. At the time of reproducing the information, it is performed by detecting the reflected light reflected by the reflective film 72. Next, the variable absorption film 7 9 1, 7 9 2 is a material which can be used in B i ₂ 0 ₃ in the characteristics of the optical recording medium of the present embodiment will be described in more detail. Figure 3 is a diagram representing the 5 0 ° C and ₂ 5 0 ° B i 2 〇 ₃ results were measured boss spectral characteristics of the absorption rate of the C. By a vacuum deposition method B i ₂ 0 ₃ thin film sample (having a thickness of 8 0 OA) in a quartz glass surface is irradiated with light dispersed by the spectroscope, to measure the absorption rate. From this measurement result, it can be confirmed that when the film temperature rises from 50 ° C to 250, the absorption edge moves to the longer wavelength side, and the wavelength λ0 of the recording light and reproduction light is set to, for example, 405 nm. By setting, you can confirm that recording and playback of information is possible Furthermore, the results of measurement of the temperature characteristics of the absorption rate by applying light having a wavelength of 4 0 5 nm to B i ₂ 〇 ₃ film for the measurement in FIG. From these results, it was confirmed that the absorptance increased as the temperature rose and exhibited an absorptivity of about 80% at 500 ° C.

From the above results, when the variable absorbing films 791 and 792 are formed using such materials, the variable absorbing films 791 and 792 have low absorption at room temperature at the start of light spot irradiation. Depending on the rate, a part of the incident light is absorbed, and the temperature rises with the absorption of the light. This rise in temperature increases the absorptance, and further light absorption raises the temperature. As described above, the light absorption increasing portion 741 is formed in the area where the light spots of the variable absorption films 791 and 792 are irradiated, and the heat generated in this area is diffused to the recording film to perform recording. Recording marks can be formed on the film. According to such a recording method, energy necessary for recording can be secured even in a multilayer optical recording medium, and a large capacity can be realized. In addition, since the light absorption increasing portion 741 formed in the variable absorption films 791 and 792 has a large extinction coefficient, the reflection at the interface with the recording films 721 and 7222 is large. The rate is also increased, and a sufficient amount of reproduced light can be obtained.

In the present embodiment, an optical recording medium having three recording layers stacked is described, but the number of recording layers is not limited to this, and it is sufficient that at least two recording layers are included. Further, the film configuration of the final recording layer 754 is not limited to this, and may have the same film configuration as the first recording layer 751 and the second recording layer 752.

In addition, in the optical recording medium of the present embodiment, the reflectivity of each recording layer and the reflectivity of each recording layer are varied so that the amount of light absorbed by each recording layer is almost the same regardless of the number of layers from the light incident side. It is preferable to set the absorption rate of the absorbing film. It is not necessary to change the recording light intensity for each target recording layer. is there. For example, in the optical recording medium of the present embodiment, the final recording layer 754 has a film configuration having variable absorption films 791 and 792, like the first recording layer 751 and the second recording layer 752. In some cases, it is preferable that the reflectance of each of the recording layers 75 1 and 752 and the absorptance of each of the variable absorption films 79 1 and 79 2 have the following relationship. Incidentally, in the following relationship, the first reflectance of the recording layer 7 5 1 and Hache absorptance of the variable absorption film 7 9 1 have R, the reflectance of the second recording layer 7 52 R _2, variable absorption the absorptivity of the film 7 92 and a _2, the peel morphism of the final recording layer 7 54 scale _3, the absorption rate of the variable absorption film and a _3. A _x = A _3/3

R 2 ^ R 3 / ^

A ₂ = A _3/2

If the recording layer and the variable absorption film are formed so as to substantially satisfy the above relationship, the intensity of the recording light can be made substantially constant regardless of the recording layer.

Further, in the present embodiment, the variable absorption films 791 and 792 are formed of a material that slightly absorbs the light L0 having the wavelength λ0 at room temperature, but has the wavelength λ0 at room temperature. It may be formed of a material transparent to light L0 (a material having a spectral absorption characteristic as shown in FIG. 5). In this case, the recording films 721 and 722 are formed of a material (for example, TeOx or Te—O—Pd) that shows a slight absorption of the light L0 having the wavelength λ0 at room temperature. As a result, heat is generated at the start of light spot irradiation by the recording films 721 and 722, and the heat is used to raise the temperature of the variable absorption films 791 and 792, thereby causing the variable absorption films 791 and 792 to increase. And the variable absorption films 791 and 792 are formed with absorption increasing portions 741. By forming the variable absorption films 79 1, 792 and the recording films 72 1, 722 in this way, the absorptance of light of wavelength λ 0 can be changed rapidly, so that the selection of each recording layer can be made more reliable. Can be done. Further, according to the optical recording medium of the present embodiment, reproduction of a recording mark below the diffraction limit, that is, so-called super-resolution reproduction becomes possible. Hereinafter, super-resolution reproduction for the optical recording medium of the present embodiment will be described.

FIG. 8 is a cross-sectional view illustrating a method for performing super-resolution reproduction using the optical recording medium of the present embodiment. FIG. 8 shows a state where light is focused on the first recording layer 751. In the optical recording medium of the present embodiment, it is possible to make the absorption increasing portion 741 formed in the variable absorption film 791 smaller than the spot size of the light L0. FIG. 9 shows the relationship between the light intensity, the extinction coefficient of the variable absorption film, and the light spot area. When light is applied to the optical recording medium of the present embodiment, the light intensity distribution in a normal condensed state has a unimodal shape close to a Gaussian function as shown in FIG. Therefore, in a state where the extinction coefficient is not saturated in the variable absorption film 791, that is, in a state where the extinction coefficient increases due to a temperature rise, the extinction coefficient of the variable absorption film 791 is a light having a large light intensity. It is larger at the center of the spot and smaller at the periphery. Therefore, by controlling the light intensity so that the light absorption increasing portion 741 formed in the portion where the extinction coefficient becomes large is formed smaller than the spot size of the light L0, as shown in FIG. Such super-resolution reproduction can be realized.

(Embodiment 2)

FIG. 6 shows a cross-sectional configuration of an optical recording medium according to Embodiment 2 of the present invention. This optical recording medium includes a substrate 711, a variable absorbing film 793 functioning as a first recording layer, a variable absorbing film 794 functioning as a second recording layer, and a final The recording layer 754 is a multilayer optical recording medium provided in this order. Separation layers 731 and 732 are provided between the recording layers. The variable absorption films 793 and 794 are the recording film 72 1 and the variable absorption film 791, the recording film 722 and the variable absorption film of the optical recording medium (see FIG. 1) of the first embodiment. 7 9 2 is realized by one film each. Separation layers 7 3 1, 7 3 Since the second and final recording layers 754 are the same as those of the optical recording medium of the first embodiment, the description is omitted here.

The variable absorption films 793 and 794 according to the present embodiment have the same characteristics as the variable absorption films 791 and 792 in the optical recording medium according to the first embodiment, and furthermore, have an optical characteristic when the temperature rises to a predetermined temperature. Is formed of a material having the property of changing. Specific examples of such a material include, for example, As ₂ S ₃ . FIG. 7 is a diagram showing the results of measuring the spectral characteristics of the As ₂ S ₃ absorptance. A sample in which an As ₂ S ₃ thin film (thickness 10 ^ m) was formed on the quartz glass surface by the vacuum evaporation method was irradiated with light separated by a spectroscope, and the absorptance was measured.

From this measurement result, it can be confirmed that when the film temperature rises from 30 ° C to 200 ° C, the absorption edge moves to the longer wavelength side. When the variable absorption films 793 and 794 are formed using As ₂ S ₃ , if the wavelength of the recording light and the reproduction light is, for example, 630 nm, the absorption rate is approximately 5% at 30 ° C. However, at 200 ° C, the absorption increases to about 60%. As a result, similarly to the first embodiment, the light absorption increasing portion 741 is formed in the area of the variable absorption film 793, 794 irradiated with the light spot, and heat is generated in this area. In addition, information is recorded by raising the temperature of the variable absorption films 793 and 794 to a temperature equal to or higher than the melting point of As ₂ S ₃ (300 ° C.) and rapidly cooling to form an amorphous phase portion. This amorphous phase portion becomes a recording mark. Information is erased by raising the temperature of the variable absorption films 793 and 794 to the crystallization temperature of As ₂ S ₃ , removing the temperature, and transforming the amorphous phase into a crystalline phase. Reproduction of information recorded on the variable absorption films 793 and 794 is performed in the same manner as in the first embodiment by using light having such a power that a recording mark is not formed on the variable absorption films 793 and 794.

As described above, according to the optical recording medium of the present embodiment, the multilayer optical recording medium Even in this case, the energy required for recording can be secured, and a large capacity can be realized. Further, since the light absorption increasing portion 741 has a large extinction coefficient, the reflectance increases, and a sufficient reproduction light amount can be obtained.

In the present embodiment, the case where 630 nm is used as an example of the wavelength λ 0 of the recording light and the reproduction light has been described. However, the present invention is not limited to this. This can be realized by appropriately selecting the materials of 793 and 794. For example, when the wavelength lambda 0 and 4 0 5 nm _{is, T e 0 2 - C a} O- W_〇 variable absorption film 7 with a mixed glass of ₃ 9 3, 7 9 4 can be formed.

Also, in the optical recording medium of the present embodiment, super-resolution reproduction can be performed similarly to the optical recording medium of the first embodiment.

Further, in the present embodiment, the case where the number of recording layers is three has been described, but it is sufficient that at least two recording layers are included, and further multi-layering is possible.

Industrial applicability

ADVANTAGE OF THE INVENTION According to the optical recording medium, the optical information processing apparatus, and the optical recording / reproducing method of the present invention, even if it is a multilayer optical recording medium including a plurality of recording layers, energy required for recording can be ensured, and Can be realized. Furthermore, when reproducing the recorded information, a sufficient amount of reproduced light can be obtained.

Claims

The scope of the claims

1. A multilayer optical recording medium including a plurality of recording layers for recording or reproducing information by irradiation with light having a wavelength λ 0,

At least one of the plurality of recording layers includes a variable absorption film,

The variable absorption film includes a material in which the energy of electrons has a band structure, and the absorption edge of the absorption spectrum moves to the longer wavelength side as the temperature rises in light absorption due to transition between bands of electrons; and When the film temperature is the first temperature, the film has the first absorptance for light having the wavelength λ 0, and when the film temperature is the second temperature higher than the first temperature, the wavelength λ 0 An optical recording medium having a second absorptance higher than the first absorptance for light having the following.

2. The optical recording medium according to claim 1, wherein the variable absorption film absorbs, at the first temperature, light having a wavelength of λ 0 by light absorption due to an interband transition of electrons in the material.

3. The recording layer including the variable absorption film further includes a recording film, and the recording film is disposed close to the variable absorption film to the extent that heat of the variable absorption film can be transmitted, 2. The optical recording medium according to claim 1, wherein the optical characteristics change at a predetermined temperature.

4. The optical recording medium according to claim 1, wherein the variable absorption film changes optical characteristics at a predetermined temperature.

5. The optical recording medium according to claim 1, wherein the first temperature is a use environment temperature of the optical recording medium.

6. The plurality of recording layers include an η layer (η is an integer of 2 or more), each of the plurality of recording layers includes the variable absorption film, and an m-th layer from the light irradiation side. When the recording layer of an eye (m is an integer of l <m≤n) is the m-th recording layer, at the first temperature, the reflectance R _m of the m-th recording layer with respect to light having a wavelength λ0 and the The absorption rate A _m of the variable absorption film included in the m-th recording layer is

A _m = A _n / (n-m + 1)

2. The optical recording medium according to claim 1, satisfying the following relationship.

7. The variable absorption film, and B i ₂ 0 _3, and A s ₂ S _3, and mixed glass containing Te 0 ₂ and N a ₂ 0, and mixed glass including T e 0 ₂ and WO _3, T E_〇 a mixed glass including ₂ and F e ₂ 〇 _3, a mixed glass including a T e O ₂ and C u 0 and including mixing glass, T E_〇 _2, C A_〇, and WO _3, a 1 2. The optical recording medium according to claim 1, comprising at least one selected from the group consisting of a GaAs compound semiconductor and an A1GaInAs compound semiconductor.

8. A multilayer optical recording medium including a plurality of recording layers for recording or reproducing information by irradiation with light having a wavelength λ 0,

At least one recording layer of the plurality of recording layers includes: a variable absorption film; and a recording film disposed close to the variable absorption film so that heat of the variable absorption film can be transmitted. ,

The variable absorption film includes a material in which the energy of electrons has a band structure, and the absorption edge of the absorption spectrum moves to the longer wavelength side as the temperature rises in light absorption due to transition between bands of electrons; and When the film temperature is the first temperature, the film is transparent to light having the wavelength λ0, and when the film temperature is the second temperature higher than the first temperature, the light having the wavelength λ0 is absorbed,

An optical recording medium characterized in that when the film temperature is the first temperature, the recording film absorbs at least a part of the light having the wavelength λ 0 and generates heat, and the optical characteristics change at a predetermined temperature.

9. The optical recording medium according to claim 8, wherein the first temperature is a use environment temperature of the optical recording medium.

1 0. The variable absorption film, and B i ₂ 〇 _3, and A s ₂ S _3, and mixed glass including T e 0 ₂ and N a ₂ 〇, a mixed glass including T e 0 ₂ and WO ₃ , a mixed glass including T E_〇 ₂ and F e ₂ 〇 _3, a mixed glass including T E_〇 ₂ and C uO, a mixed glass including T e 0 _2, C a O, and WO _3, a 1 9. The optical recording medium according to claim 8, comprising at least one selected from the group consisting of a GaAs compound semiconductor and an A1GaInAs compound semiconductor.

1 1. The optical recording medium according to claim 1 or 8,

A light source that emits light having a wavelength λ 0,

A condensing optical system that condenses the light emitted from the light source on a target recording layer included in the optical recording medium;

A light detector for detecting light reflected by the optical recording medium; and forming a light absorption increasing portion in the variable absorption film by irradiating the light emitted from the light source; and a temperature of the light absorption increasing portion. An optical information processing apparatus, which records or reproduces information by raising the optical information.

1 2. A control unit for controlling the intensity of light emitted from the light source so that the light absorption increasing portion formed on the variable absorption film is smaller than the spot size of the light to be collected. The optical information processing device according to claim 11, which includes the optical information processing device.

1 3. An optical recording and reproducing method for recording and reproducing information on and from the optical recording medium according to claim 1 or 8,

By condensing light having a wavelength λ0 on a target recording layer, forming a light absorption increasing portion on a variable absorption film included in the recording layer, and increasing the temperature of the light absorption increasing portion, the recording is performed. Features recording and reproducing information on layers Optical recording / reproducing method.

14. The method according to claim 13, wherein the intensity of the light is controlled such that the light absorption increasing portion formed on the variable absorption film is smaller than a spot size of the light to be condensed. Optical recording and reproduction method.